Disclosed are methods of producing calcined coke from bio-oil from a biomass feedstock, involving (1) subjecting the bio-oil to atmospheric distillation in a batch or continuous distillation unit and/or subsequently to vacuum distillation in a batch or continuous vacuum distillation unit to produce coke (i.e. distillation bottoms), (2) subjecting the coke bottoms to (a) stepwise calcination at about 400° to about 1000° C. for about 1 to about 30 minutes in an inert gas atmosphere in a reactor to produce devolatilized coke, optionally cooling the devolatilized coke, removing the devolatilized coke from the reactor and optionally crushing the devolatilized coke, and stepwise calcining the devolatilized coke at about 1200° C. to about 1400° C. for up to about 2 hours in an inert gas atmosphere in a reactor to produce calcined coke; or (b) devolatilization at about 400° to about 1000° C. for about 1 to about 30 minutes in an inert gas atmosphere in a reactor to produce devolatilized coke and stepwise calcining the devolatilized coke at about 1200° C. to about 1400° C. for up to about 2 hours in an inert gas atmosphere in the same reactor to produce calcined coke; or (c) stepwise heating at about 250° to about 400° C. for about 2 to about 10 hours, then subsequent stepwise calcination at about 400° to about 1000° C. for about 0.5 to about 5 hr to produce devolatilized coke, then calcining said devolatilized coke at about 1200° C. to about 1400° C. for about 1 to about 4 hours in an inert gas atmosphere in a batch or continuous reactor to produce calcined coke; or (d) stepwise calcination in a continuous calcining reactor between about 200° to about 1400° C. with up to about 1 hr residence time. Also disclosed are calcined cokes produced by such methods.
Since the worldwide consumption of liquid transportation fuels is outpacing the finite supply of fossil fuels, research for petroleum replacements have focused squarely on fuels (Mangla, V. et al., Curr. Chem. Biol., 7: 96-103 (2013); Sorrell, S., et al., Energy Policy, 38: 5290-5295 (2010)). Although finished motor fuels comprise the bulk of petrochemical refinery outputs, the world economy relies heavily on many everyday products that emanate from petroleum (U.S. Environmental Protection Agency, http://www.eia.gov/dnav/pet/pet_cons_psup_dc_nus_mbbl_a.htm). Some basic examples include commodity chemicals like BTEX petrochemical feedstock (benzene-toluene-ethylbenzene-xylenes), phenolic resins for plastics, waxes and lubricants, and asphalt for roofing and road pavement. Altogether, non-fuels co-products comprise 15-20% of all petroleum products (U.S. Environmental Protection Agency, http://www.eia.gov/dnav/pet/pet_cons_psup_dc_nus_mbbl_a.htm). Furthermore, many petrochemical refineries rely on non-fuels applications for the large majority of their product sales. Therefore, a strategy for renewable fuels must be coupled with a strategy to bring economic value via petrochemical co-product replacements. As an example, production of biodiesel was found to be economically viable due to the feasibility of producing glycerol in parallel (Haas, M. J., et al., Bioresource Technol., 97: 671-678 (2006); Lopes, D. C., et al., Energ. Econ., 40: 819-824 (2013)).
One of the most crucial yet least discussed co-products of value is petroleum coke (termed “petcoke”). Typically, the residuals remaining after vacuum distillation of crude oil (>600° C.) enter a delayed coker unit which thermally cracks the residual into petcoke and lighter fuel components (Olsen, T., “Chemical and Engineering Practice,” An Oil Refinery Walk-Through, pp. 34-40, May 2014). Petcoke can be used as-is to substitute for coal in fuel applications or, if the metals and sulfur contents are low enough, can be calcined into coke products suitable for use in aluminum smelting anodes. The latter application alone can absorb more than 70% of the petcoke market (Zhang, Z., and T. Wang, J. Therm. Sci. Eng. App., 2: 021006-1-021006-8 (2010); Ellis, P. J., and C. A. Paul, “Tutorial: Petroleum Coke Calcining and Uses of Calcined Petroleum Coke,” IN AIChE 2000 Spring National Meeting,Third International Conference on Refining Processes, Session T9005, Atlanta, Ga., 2000). Other high-volume markets for calcined coke utilize the remaining 30% for production of graphite, steel, and titanium dioxide (Ellis and Paul 2000; Paul, C. A., and L. E. Herrington, “Desulfurization of petroleum coke beyond 1600° C.” IN Light Metals: Proceedings of Sessions, TMS Annual Meeting, Warrendale, Pa., 597-601, 2001). Globally, 50 M metric tons/year of aluminum are produced from approximately 25M metric tons of carbon per year, and low-quality coke can cost smelters more than $100/metric ton of product in consumption costs (“The carbon anode market-a global viewpoint (Interview with Michael Wrotniak, CEO of Aminco Resources),” Aluminum, June 2014; Alcoa Inc., “Aluminum smelting technical article,” http://www.alcoa.com/global/en/about_alcoa/pdf/Smeltingpaper.pdf). Petcoke demand continues to rise annually, for which the U.S. provides more than half the global supply, and the market has gone wanting for sources that are renewable due to several sustainability factors (“Asian demand spurs U.S. net exports of petroleum coke to higher levels in early 2012,” Petroleum Supply Monthly, U.S. Energy Information Administration, 25 May 2012, http://www.eia.gov/todayinenergy/detail.cfm?id=6430#; Chmelar, J., Size reduction and specification of granular petrol coke with respect to chemical and physical properties, Doctoral thesis, Norwegian University of Science and Technology, 2006). Although aluminum smelting can tolerate 2-3% sulfur, further reduction of sulfur is desired due to the corrosive nature of sulfur during the smelting process, which reduces anode lifetime (Edwards, L., “Impurity level distribution in gpc and cpc and impact on anode properties,” IN Light Metals 2014: The Minerals, Metals, & Materials Society, Wiley, 2014, pp. 1093-1098). Even 1% sulfur ruins steel mechanical properties through brittleness. Demand for high-quality calcined coke is hampered by the continually declining quality of petcoke, via high sulfur and metals content (Ni, V)(Edwards, L. C., “Responding to Changes in Coke Quality,” IN Proceedings of the 10th Australian Smelting Technology Conference, Terrigal, NSW, 2007; Edwards, L. C., et al., “A review of coke and anode desulfurization,” IN Light Metals, Wiley, 2007). Calciners currently must desulfurize coke to meet demand for both anodes and steel, which intensively increases processing costs.
Extremely high temperatures and/or pressures are required to initiate and propagate coke polymerization. Hence, one cannot easily produce coke as a side product from enzymatic processes for cellulosic ethanol or lipid-based biodiesel processes since they operate under mild conditions (i.e., low temperature and pressure). While coke does come about as a side product in hydrodeoxygenation, coke deactivates catalysts and blocks catalyst pores, which makes coking an unwanted phenomenon in situ. Incidentally, thermochemical methods of biofuels production (e.g., gasification, pyrolysis) are well-suited for isolating biochar solid residue in parallel to the liquid crude oil that is produced (“bio-oil”). However, the high metals content of biochar renders it unsuitable for refined coke and much more amenable for soil remediation (Gurtler, J., et al., Foodborne Pathog. Disease, 11: 215-223 (2014)). When bio-oil is distilled, the solid residue that remains leftover could serve as a precursor for biorenewable calcined coke. Traditional bio-oil distillation had been largely ignored due to significant yield losses from thermal instabilities. Recently, we demonstrated the high-yield distillation of tail-gas reactive pyrolysis (TGRP) bio-oil under normal atmospheric distillation conditions (Elkasabi, Y., et al., ACS Sustainable Chem. Eng., p. 10.1021/sc5002879 (2014)). The TGRP process does not utilize any catalyst nor external hydrogen, yet surprisingly produces bio-oils with <10 wt % oxygen, comparable to catalytic fast pyrolysis bio-oil (vs. 34-40 wt % in traditional bio-oil produced by traditional fast pyrolysis), which gives rise to thermally stable bio-oils for distillation (Mullen, C. A., et al., Energy Fuels, 27: 387-3874 (2013)). Solid residues remaining post-distillation amount to >15% of the starting bio-oil, which amounts to a significant profit if it can be processed into suitable petroleum coke.
Herein we discuss bio-oil distillate bottoms as a source for renewable calcined coke in various applications.